Observation and Analysis of Repeating Earthquakes beneath the Aceh Basin, Northern Sumatra

Open Access
Barrett, Sarah Anne
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Charles James Ammon, Thesis Supervisor
  • Peter J Heaney, Honors Advisor
  • Earthquakes
  • seismology
  • Sumatra
  • subduction
  • repeating earthquakes
Repeating earthquakes are observed across a variety of tectonic settings. In this study we discuss observations of numerous repeating earthquakes that occurred beneath the Aceh Basin following The Great 2004 Sumatra-Andaman Earthquake. The Aceh Basin is the northernmost in a series of forearc basins located along the Sunda Trench (~94° E, 5° N). The plate boundary beneath the basin was relatively aseismic prior to the 2004 megathrust earthquake. An analysis of the moderate-size earthquakes occurring beneath the Aceh Basin in response to the 2004 megathrust provides interesting and important observations of stick-slip faulting near the deep within the seismogenic zone. We use teleseismic and distant regional observations to identify repeating earthquakes that we infer to be located along the plate boundary 30-50 km beneath the seafloor. Analysis of the short-period coda following teleseismic and regional P and regional S waves is used to estimate the distance between repeating events in the same sequence. The coda analysis indicates that in most instances the same asperity is failing in the sequence of repeating events. Despite incredibly consistent coda coherence, events within each sequence show resolvable amplitude differences, which suggest changes in frictional strength occurring throughout the duration of the repeating earthquake sequence. This rapid change (over a few seismic cycles) in strength may be a function of the erosion of the asperity or a change in intrinsic strength. Additional studies of large aftershock sequences, such as the 2010 Chile earthquake, may provide more insight into these questions.